Spiral wound filter and method of making same

ABSTRACT

The fluid filter (10) for fuel has a wound filter element (17) arranged in the housing (11) surrounded on its bottom end face (22) by a funnel-shaped welded-on cover cap (18). The cover cap (18) made of thermoplastic has an annular welding surface (25) which extends perpendicularly relative to the longitudinal axis of the filter and which is welded at least to the outermost complete turn (29) of the winding (17). An adhesive-free connection (32) between the wound filter element (17) and housing (11) thereby is formed. The preassembled wound filter element (17, 18) which can be handled easily is suitable for cold assembly on universal production lines and for different models.

BACKGROUND OF THE INVENTION

The invention relates to a fluid filter for a fuel.

A known fuel filter includes a housing having at least one inletconnector and at least one outlet connector for a fluid to be filtered,a middle tube located in the housing, a filter element arranged in thehousing, the filter element consisting of a band-shaped filter materialwound spirally around the middle tube to form a plurality of completeturns including an outermost complete turn, opposing end faces of thefilter element on opposite ends thereof and spaces between the turns,which open towards the opposite end faces and which communicate with theconnectors, and a bottom cover cap which engages the filter element.

Such a fluid filter is already known from WO-Al 0, 081, 597, especiallyFIG. 2. In this fuel filter a wound filter element is arranged in ahousing and has a funnel-shaped cover cap on its bottom end face on theclean side of the fuel filter. This cover cap deflects the purifiedfluid flow coming out of the end face into the middle tube. At the sametime, inwardly pressed radial ribs supporting the filter element arearranged in the cover cap. A disadvantage of this fluid filter is thatthis cover cap consists of metal and has a sleeve-shaped edge portionwhich is widened in a funnel-shaped manner and into which the woundfilter element is simply pressed with its outer surface. By this simplepressing of the filter element into the cover cap, a serviceable sealingbetween the dirty side and clean side of the filter can be achieved, inthe region of the compressed outer surface, only with oils havingsubstantially higher viscosities than petrol or diesel fuels. Moreover,when the filter element is being pressed in, the outer layers of thewinding usually consisting of paper are excessively compressed or evendamaged. Furthermore, the metal cover cap necessitates an increasedoutlay in terms of material and machining. Besides, the distance betweenthe cover cap and the bottom of the housing not only results in a poorutilisation of space, but is also unsuitable for different models inwhich an additional connection has to be provided at the bottom of thehousing. In addition, because of the assembly of a large number ofindividual parts, the construction of the filter is cost-intensive.

Further, German Patent Specification 3,513,062 makes known a fluidfilter, in the housing of which a wound filter element is arranged withthe help of a cover cap. Here, the wound filter element and the covercap are already appropriately preassembled with one another in afluid-tight manner. A disadvantage, however, is that the cover cap isarranged on the upper end face of the wound filter element and thiscover cap bounds with a housing lid an additional inflow space.Moreover, in this design of the cover cap a series of sealing pointsbetween the dirty side and clean side are necessary. At the same time,one of these sealing points between the cylindrical outer surface of thewound filter element and an associated cylindrical inner wall at atubular extension of the cover cap can be produced only with difficulty,especially as there is no axial fixing of these two parts relative toone another. Besides, an additional adhesive bond is required betweenthe filter insert and filter housing to separate the dirty side andclean side.

Further, German Patent Specification 2,256,995 makes known a fluidfilter with a wound filter element, in which the prefabricated filterelement is bedded into the bottom-shaped housing lower part. Here, theprefabricated filter element possesses, on its cylindrical outersurface, a preformed annular bead of hot-melt adhesive which isoversized in relation to the inner wall of the housing and which, whenthe wound filter element is pressed into a heated housing part, melts inits outer edge zone and, after solidifying, makes a firm sealingconnection between the dirty side and clean side. But it can be adisadvantage that this connection between the filter winding and housingis possible only by an adhesive. For a perfect connection, thebowl-shaped housing part must be cleaned so as to be absolutely free ofgrease before the wound filter element is bedded in, thereby increasingthe production outlay. During any intermediate storage of the filterelement, its two end faces are exposed without protection tocontamination.

SUMMARY OF THE INVENTION

According to the invention, the bottom cover cap is made ofthermoplastic and has a peripheral welding surface which extendstransversely relative to the longitudinal axis of the filter, and atleast the outermost complete turn of the filter element is connectedsealingly to the welding surface of the cover cap. The advantage of thefluid filter according to the invention, s that it allows anadhesive-free connection between the wound filter element and thehousing which makes reliable sealing possible, whilst at the same timebeing of relatively simple design. Here too, the filter element and thecover cap can be preassembled, with the result that it is especiallysuitable for mass production, in which only cold assembly is nownecessary on the production line. Moreover, this adhesive-freeconnection is suitable for fluid filters of different models, such as,for example, a conduit filter or a box filter with or without a wateroutlet connection. The cover cap can be fastened to the wound filterelement cost-effectively and thus leads to a storable intermediateproduct which can be handled easily and which is especially suitable forautomatic line production. The complete housing interior is the dirtyside, so that only a low washing quality is necessary for the housing.Moreover, the wound filter element is resistant to fuels with a highmethanol or ethanol content.

When the cover cap is provided with a circumferential step on which thewelding surface is located and the radial width of the welding surfacecorresponds at least to the thickness of two turns of the filterelement, the quality of the connection point achieved has a high degreeof reliability at a low outlay. Furthermore, the cover cap can be shapedto fit the bottom member of the housing so as to bear on a substantialportion of the bottom member, as a result of which favourably locatedsealing points can be obtained, in addition to a good utilization ofspace and increased stability. Advantageously a plurality of radial ribscan be provided in the cover cap in the same plane as the weldingsurface. Moreover, it becomes simpler to produce an intermediate productif a suitable exterior surface is provided on the cover cap. It isextremely advantageous if the wound filter element is produced in thecover cap by heated-tool welding. Advantageously, a napped, trap filtercan also be incorporated.

BRIEF DESCRIPTION OF THE DRAWING

Three exemplary embodiments of the invention are illustrated in thedrawing and explained in more detail in the following description.

FIG. 1 shows a longitudinal section through a first fluid filter in asimplified representation and designed as a conduit filter,

FIG. 2 is a detailed cross sectional view of a connection point of thewound filter element to the cover cap according to FIG. 1,

FIG. 3 is a detailed cross sectional view of a cutaway portion of thecover cap before the filter element is welded in,

FIG. 4 shows a longitudinal section through a second fluid filterdesigned as a box filter, and

FIG. 5 shows a longitudinal section through part of a third fluid filterdesigned as a box filter with a water storage space;

FIG. 6 is a detailed cross sectional view of a lower portion of a fourthfluid filter including the connection point of the wound element to thecover cap.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

FIG. 1 shows a first fluid filter 10, the housing 11 of which consistsessentially of a bowl-shaped housing part 12 and a lid 13 which areconnected sealingly and firmly to one another at a flanged point 14.

The fluid filter 10 is designed as a conduit filter, for which purposeit possesses, at opposite ends of the housing 11, two connectors 15, 16,of which the first connector 15 in the lid 13 serves as an inlet for thefluid flow, whilst the second connector 16 on the bottom of the housingpart 12 is used as an outlet.

The housing 11 receives inside it a filter element 17 through which theflow passes axially and which is connected sealingly and firmly to abottom cover cap 18. The filter element 17 consists in a way known perse of a wound web of filter material of V-shaped cross-section which iswound spirally round a middle tube 19, with an adhesive added, so thattwo spaces engaging in one another spirally and each being open towardsone end face 21, 22 are formed in the filter element 17. The middle tube19 is closed by a plug 23 at its end on the dirty side of the filter andtherefore to the first end face 21. A closed middle tube made of plasticcan also be used.

As shown in more detail in FIG. 2, between the filter element 17 and thecover cap 18 there is an adhesive-free connector, in that the two partsare welded to one another. For this purpose, the cover cap 18 consistsof a thermoplastic, especially polyoxymethylene (POM). The cover cap 18possesses in the vicinity of its outer edge, a circumferential step 24,which extends perpendicularly relative to the longitudinal axis of thefluid filter 10 and on which is formed an annular welding surface 25facing the second end face 22 and extending essentially horizontally.The cover cap 18 merges from the circumferential step 24 into an axiallyextending sleeve-like peripheral portion 26 which has a conical innerwall 27. Furthermore, on the cover cap 18 an exterior surface 28 isformed on the circumferential step 24 opposite to the welding surface25. The width of the annular welding surface 25 is preferably selectedas being so large that, on the filter element 17, the paper pocketsassociated with the two outer complete turns 29 are fastened sealinglyin the welding surface 25. Moreover, within the sleeve-shaped peripheralportion 26 a short portion of the outer surface 31 of the filter element17 is also welded to the conical inner wall 27 of the cover cap 18. Onthe second end face 22 located on the clean side, the filter element 17is supported, in the region between the welded paper pockets and themiddle tube 19, on ribs 33 which here are arranged radially in the covercap 18. The welding surface 25 and the top edges of the ribs 33 thus lieessentially in a plane extending perpendicularly relative to thelongitudinal axis of the filter 10, so that the axial position of thefilter element 17 relative to the cover cap 18 is fixed.

The adhesive-free connector between the filter element 17 and the covercap 18 is made as follows, FIG. 3 being referred to in more detail. FIG.3 shows part of the cover cap 18 before the welding operation on anenlarged scale. The cover cap 18 consisting of thermoplastic possesses,in the region of the welding surface 25 and also in the region of theinner wall, material elevations 34, 35 which are melted by means of anintroduced heating punch 36. After the heating punch 36 has been pulledout of the cover cap 18, the filter element 17 is pressed into the stillmelted material elevations 34, 35, until its end face 22 rests on thewelding surface 25 and also the ribs 33. The melted plastic, aftersolidifying, produces a firm sealing connector point 32. Forcounterpressure while the filter element 17 is being pressed in anexterior surface 28 is arranged on the cover cap 18, so that the forcesarising are compensated directly in the region of the step 24. Thepreassembled filter element 17 can be handled easily and is especiallysuitable for further processing on production lines of universal use.

As FIG. 1 also shows, the shape of the cover cap 18 is so designed thatit bears on a bottom member 37 of the bowl-shaped housing part 12 over amajor portion of the bottom member. Furthermore, the cover cap 18 has acentrally formed tubular connector piece 38, by means of which itprojects into a matching outwardly open housing connector piece 39 ofthe bowl-shaped housing part 12. Arranged in the plastic tubularconnector piece 38 is a metal threaded nut 41 which can easily beinserted during the production of the cover cap 18 by injection molding.

During the production of the fluid filter 10, the prefabricated filterelement 17 is inserted with its welded on cover cap 18 into thebowl-shaped housing part 12, and thereafter the housing part 12 isflanged with the lid 13. The unfiltered fuel supplied at the firstconnector 15 flows axially through the filter element 17 and at thesecond end face 22 passes purified over into the space of the cover cap18 through which the ribs 33 extend, and flows further to the secondconnector 16. Unfiltered fuel which seeps through between the inner wallof the bowl-shaped housing part 12 and the filter element 17 cannot passinto the cover cap 18 on the clean side, since the tightening of thethreaded nut 41 during the assembly of the fluid filter 10 ensures areliable sealing between the threaded nut 41 and the housing part 12. Asa result of this adhesive-free connector 32, therefore, the outlay forcleaning the housing part 12 before the preassembled filter element 17is installed can also be kept low, especially as dirt which mayinfiltrate is trapped between the cover cap 18 and bottom member 37 andcannot reach the clean side in the second connector 16.

FIG. 4 shows, in simplified representation, a longitudinal sectionthrough a second fluid filter 50 which differs as follows from the firstfluid filter 10 according to FIG. 1, like reference symbols being usedfor the same components.

The second fluid filter 50 is designed as a box filter, such as is usedfor fuel filtering in diesel series pumps. In it, the two connectors 15and 16 are arranged together in the lid 51, so that there is no need foran outlet in the bottom member of the housing part 12. Correspondingly,the cover cap 52 is also designed without a central orifice and has acontinuous bottom member. The unpurified fuel in flowing at the firstconnector 15 comes out purified on the second end face 22 of the filterelement 17 and is guided by the cover cap 52 into a channel 53 of themiddle tube 19 and further to the second connector 16.

FIG. 5 shows a longitudinal section through part of a third fluid filter60 which differs as follows from that according to FIG. 4, likereference symbols being used for the same components. The third fluidfilter 60, like the second fluid filter 50, is designed as a box filter,in which the two connectors 15, 16 are located in the lid 51, andadditionally has a water storage space 61. This water storage space 61can be obtained in a simple way by increasing the constructional lengthof the cover cap 62 in the axial direction by a tubular extended part 63and by also enlarging the ribs 33 correspondingly. Moreover, the covercap 62 has a water outlet 64, for which purpose the thread 65 forreceiving a suitable water outlet screw can be arranged directly in thetubular connector piece 38 consisting of plastic.

The functioning of the third fluid filter 60, used above all for thepurification of fuel for diesel distributor pumps, largely correspondsto that of the second fluid filter 50, and in addition the precipitatedwater can be collected in the storage space 61 and emptied via the wateroutlet 64.

FIG. 6 shows as a detail of a fourth fluid filter 70 the connector pointbetween the filter element and cover cap 71, the fourth fluid filter 70differing as follows from the first fluid filter 10 according to FIG. 2,like reference symbols being used for the same parts.

In the fourth fluid filter 70, the filter element 17 is melted into thewelding surface 25 in the axial direction only, so that there is noradial sealing there. This makes production easier, since the heatingpunch 36, when being introduced, does not have to melt any radial wall.Furthermore, the width of the step 24 and therefore of the annularwelding surface 25 is selected as larger, and additionally arranged inthe plane of the welding surface 25 is a napped trap filter 72 made ofpaper or a non-woven, which, during welding, is melted in with its outeredge in the same operation.

It is possible, of course, to make changes to the embodiments shown,without departing from the idea of the invention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this invention.

What is claimed is new and desired to be protected by Letters Patent isset forth in the appended claims.
 1. In a fluid filter including ahousing having an inlet connector and an outlet connector for a fluid tobe filtered, a middle tube located in the housing, a filter elementarranged in the housing, the filter element consisting of a band-shapedfilter material wound spirally around the middle tube to form aplurality of complete turns including an outermost complete turn and endfaces of the filter element on opposite ends thereof, and a bottom covercap which engages the filter element in the vicinity of an adjacent oneof the end faces and which connects the adjacent end face to the outletconnector, the fluid filter also having a longitudinal axis, theimprovement wherein the cover cap (18; 52; 62) is made of thermoplasticand has a peripheral welding surface (25) which extends transverselyrelative to the longitudinal axis of the filter (10), and at least theoutermost complete turn (29) of one end of said end faces of the filterelement (17) is sealingly welded to the welding surface (25) of thecover cap (18; 52; 62).
 2. The improvement as defined in claim 1,wherein the cover cap (18; 52; 62) has a circumferential step (24), thewelding surface (25) being arranged on the circumferential step (24). 3.The improvement as defined in claim 2, wherein the welding surface has aradial width and the radial width of the welding surface (25)corresponds at least to a thickness of two turns (29) of the filterelement (17).
 4. The improvement as defined in claim 2, wherein thecover cap (18; 52; 62) has a sleeve-like peripheral portion (26) havingat an at least partially conical inner wall (27).
 5. The improvement asdefined in claim 4, wherein the inner wall (27) of the cover cap (16;52; 62) is welded to an outer surface (31) of the filter element (17).6. The improvement as defined in claim 2, wherein the cover cap (18; 62;62) has an exterior surface (28) located opposite the welding surface(25).
 7. The improvement as defined in claim 1, wherein the housing hasa bottom member and the cover cap (18; 52; 62) is shaped to bear againstthe bottom member (37) of the housing (11) over a major portion of thebottom member.
 8. The improvement as defined in claim 1, wherein thecover cap (18; 52; 62) has a plurality of radial ribs (33) supportingthe adjacent end face (22) of the filter element (17).
 9. Theimprovement as defined in claim 8, wherein the welding surface (25) anda plurality of top edges of the radial ribs (33) extend essentially inone plane.
 10. The improvement as defined in claim 1, wherein the outletconnector (16) comprises an outer connector piece (39) of the housing, acentral tubular connector piece (38) of said cover cap (18), saidcentral tubular connector piece (38) of said cover cap (18) projectinginto said outer connector piece (39), and a threaded nut (41) receivedin the tubular connector piece (38).
 11. The improvement as defined inclaim 1, wherein the housing (11) comprises a housing part (12) and alid (51) closing the housing part (12) at one end of the housing (11),the two connectors (15, 16) being provided in the lid (51).
 12. Theimprovement as defined in claim 11, wherein the cover cap (62) has atubular extended part (63) forming a water storage space (61 and aplurality of radial ribs (33) located in the tubular extended part (63),said water storage space (61) being connected to a water outlet (64).13. The improvement as defined in claim 1, further comprising a nappedtrap filter (72) arranged in the cover cap (71) level with the weldingsurface (25), an outer edge of the napped trap filter (72) being meltedinto the welding surface (25).
 14. Process for making a fuel filtercomprising a housing having an inlet connector and an outlet connectorfor a fluid to be filtered, a middle tube located in the housing, afilter element arranged in the housing, the filter element consisting ofa band-shaped filter material wound spirally around the middle tube toform a plurality of complete turns including an outermost complete turnand also end faces of the filter element on opposite ends thereof, and athermoplastic bottom cover cap, which engages the filter element andwhich has a peripheral welding surface (25) which extends transverselyrelative to the longitudinal axis of the filter (10), at least theoutermost complete turn (29) of one of said end faces of the filterelement (17) being sealingly welded to the welding surface (25) of thecover cap (18; 52; 62), said process including the steps of applying aheating punch (36) to the cover cap (18; 52; 62), partially melting thewelding surface (25) with the heating punch, after said partiallymelting pressing the filter element (17) into the welding surface (25)and allowing the melting surface (25) to solidify to form a sealingconnection with the filter element.